1. Field of the Invention
The present invention relates to a wire traverse apparatus of a wire saw, and more particularly to a wire traverse apparatus of a wire saw, which slices a workpiece such as a semiconductor ingot, a ceramic, a glass, etc. into a large number of wafers by a running wire.
2. Description of the Related Art
A wire saw is one of apparatuses which slice a workpiece such as a semiconductor ingot, a ceramic, a glass, etc. into wafers. In the wire saw, a wire is supplied from one wire reel, and is wound on a plurality of grooved rollers to form wire rows. Then, the wire is wound up by the other wire reel. The processing solution including abrasive grains is supplied to the wire rows, and the workpiece is pressed on the wire row, so that the workpiece is sliced into a large number of wafers by the lapping operation of the abrasive grains.
In the above-mentioned wire saw, a wire traverse apparatus is provided near each wire reel. The wire traverse apparatus guides the wire, which is wound up the wire reel, and the wire, which is supplied from the wire reel, in the direction of the wire reel's axis.
The wire is wound up by the wire reel in a spiral, so the wire moves in the direction of the wire reel's axis when the wire is supplied from the wire reel. For example, if the wire is wound up by the wire reel irregularly, the change in the wire moving speed occurs when the wire is supplied.
On the other hand, the wire traverse apparatus is provided with a slider, which moves in the direction of the wire reel's axis. A pair of detectors are provided at a predetermined interval in the slider. The wire is arranged between these two detectors. When there is a difference in the moving speed between the wire and the slider, the wire touches one of the detectors. Then, the wire guiding speed is controlled based on a touch signal transmitted from the detector the wire touches, so that the wire no longer touches the detector.
The above-mentioned traverse apparatus controls the wire guiding speed when the wire touches the pair of detectors. There is another wire traverse apparatus, which controls the wire guiding speed based on a rotational speed of a touch roller.
In this wire traverse apparatus, a pair of touch rollers are rotatably supported by a slider at a predetermined interval. In this case, if there is a difference in the moving speed between the wire and the pair of touch rollers, the wire, which is arranged between the touch rollers, touches the touch roller. As a result, the touch rollers are rotated. Then, the number of rotations when the wire touches the touch roller is detected, and the moving speed of the pair of touch rollers for guiding the wire is controlled according to the detected number of rotations.
However, the wire traverse apparatus, which controls the wire guiding speed when the wire touches the pair of detectors, detects the gap in the moving speed between the wire and the pair of detectors. Therefore, the detectors become worn because the wire touches them, so the accuracy in detecting the speed gap lowers. Moreover, there is a time lag from the wire and the touch roller are released from each other to the rotation of the touch roller is stopped. So, there is a problem in that the pair of the touch rollers cannot quickly respond to the change in the wire moving speed. In particular, when the problem becomes more serious, a hunting occurs in the pair of the touch rollers.